Simple example of creating UI dynamically in Java

BuildUIDynamically.java

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.text.TextUtils;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.LinearLayout;
import android.widget.TextView;
import android.widget.Toast;

import java.util.Locale;

public class BuildUIDynamically extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        LinearLayout rootLayout = new LinearLayout(this);
        rootLayout.setOrientation(LinearLayout.VERTICAL);

        final EditText et1 = new EditText(this);
        et1.setHint("Enter percent");

        final EditText et2 = new EditText(this);
        et2.setHint("Enter number");

        Button btnConfirm = new Button(this);
        btnConfirm.setText("Calculate");

        final TextView tvOutput = new TextView(this);

        rootLayout.addView(et1);
        rootLayout.addView(et2);
        rootLayout.addView(btnConfirm);
        rootLayout.addView(tvOutput);

        setContentView(rootLayout);

        rootLayout.setPadding(16, 16, 16, 16);

        et1.setInputType(2);
        et2.setInputType(2);

        btnConfirm.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                String p = extract(et2), n = extract(et1);

                if (TextUtils.isEmpty(p) || TextUtils.isEmpty(n))
                    Toast.makeText(getApplicationContext(), "missing info!", Toast.LENGTH_SHORT).show();
                else
                    tvOutput.setText(calculate(Double.parseDouble(p), Double.parseDouble(n)));
            }
        });
    }

    private String calculate(double... d) {
        return String.format(Locale.getDefault(), "Answer: %.2f", (d[0] / 100) * d[1]);
    }

    public String extract(EditText et) {
        return et.getText().toString();
    }
}